LEDs are semiconductor photonic devices that emit light when a voltage is applied. LEDs have increasingly gained popularity due to favorable characteristics such as small device size, long lifetime, efficient energy consumption, and good durability and reliability. In recent years, LEDs have been deployed in various applications, including indicators, light sensors, traffic lights, broadband data transmission, back light unit for LCD displays, and other suitable illumination apparatuses. For example, LEDs are often used in illumination apparatuses provided to replace conventional incandescent light bulbs, such as those used in a typical lamp.
One of the performance criteria for LED lighting instruments involve its color appearance. For example, it is desirable for an LED lighting instrument to maintain a substantially white appearance even as it is turned off, since that is more pleasing for the human eye and better resembles a traditional non-LED lamp. However, existing LED lighting instruments often suffer from non-white appearances when they are turned off. For example, conventional LED light bulbs may still take on a yellowish appearance when they are turned off.
Therefore, although existing LED lighting instruments are generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect. An LED lighting instrument capable of producing a substantially white appearance when it is turned off continues to be sought.